Voltage stabilizing and harmonic suppression transformer systems



May 7, 1968 5, QUIMBY 3,382,427

VOLTAGE STABILIZING AND HARMONIC SUPPRESSION TRANSFORMER SYSTEMS Filed April 19, 1966 F|G.l. FIG-.2.

I I7 [7 ---a0 I8 a I 20 2o INVENTOR= ROBERTS. QUIMBY, BY (2am avm ATTORNEY United States Patent 3,382,427 VOLTAGE STABILIZING AND HARMONIC SUPPRESSION TRANSFORMER SYSTEMS Robert S. Quimby, Lexington, Mass, assignor to Stevens- Arnold Inc., South Boston, Mass. Filed Apr. 19, 1966, Ser. No. 543,682 Claims. (Cl. 323-61) This invention relates to ferro-reson-ant voltage stabilizers, and has as an object to substantially reduce harmonic voltages in the outputs of such stabilizers without increasing their costs.

AC voltage stabilizers using saturating transformers, and linear chokes are well known, being disclosed, for example, in Patents Nos. 1,985,634 and 1,985,635 of W. K. Fleming. The transformers of such stabilizers are operated at the upper bends of their magnetization curves for taking advantage of the very large variations in inductive reactance with small variations in input voltage, but such operation results in the generation of undesired, odd harmonic voltages. My joint Patent No. 2,505,620 discloses such a stabilizer having a harmonic filter for reducing such harmonic voltages.

This invention is an improvement of that disclosed in the Patent No. 2,505,620 in that voltage stabilization and reduction of odd harmonic voltages are accomplished by using fewer components, and in that transformer and choke assemblies are combined.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a circuit schematic of one embodiment of this invention;

FIG. 2 is a circuit schematic of another embodiment of this invention;

FIG. 3 is a side view of the combined choke and transformer assembly, and

FIG. 4 is a section along the lines 4-4 of FIG. 3.

A laminated core 9 of a transformer has side legs 10, has aligned center legs 11 and 12, and has a cross portion 13 extending from the side legs 10 between the center legs 11 and 12. Choke windings 14 and 16, and a voltage compensating winding 15 are around the center leg 11, the latter having a relatively wide air gap 30 between its inner end and the core portion 13. A primary winding 17, a secondary winding 18, and a voltage step-up winding are around the center leg 12, the latter having a relatively narrow air gap 19 between its inner end and the core portion 13. The core portion 13 is common to the magnetic circuits of all of the windings.

The relatively narrow air gap 19 permits the leg 12 of the core 9 to saturate at the desired operating current. The relatively wide air gap 30 prevents the leg 11 of the core 9 from saturating when the leg 12 is saturated. The air gap 19 could be located anywhere across the leg 12. The air gap 16 could be located anywhere across the leg 11.

Referring now to FIG. 1 of the drawings, one end of the primary winding 17 is connected to an input terminal 22, and to one end of the voltage step-up winding 20. The other end of the winding 17 is connected to one end of the choke winding 14, the other end of which is connected to one end of the choke winding 16. The other end of the winding 16 is connected through capacitor 26 to the other end of the winding 20. One end of the secondary winding 18 is connected to an output terminal 27, and its other end is connected to one end of the winding 15. The other end of the winding 15 is connected to output terminal 28.

The capacitor 26 connected to the primary winding 17 causes the input circuit to have capacitive reactance, and the choke winding 14 connected to the primary winding 17 causes the input circuit to have inductive reactance.

3,382,427 Patented May 7, 1968 The capacitor 26 in series with the windings 16 and 20 across the primary winding 17, is in effect, due to the relatively low impedances of the windings 16 and 20, connected across the winding 17, and forms a shunt circuit resonant at the frequency of the applied AC voltage, which may be 60 c.p.s. As the applied voltage increases from zero voltage, both the choke winding 14 and the transformer winding 17 exhibit inductive reactance, and the current in the input circuit increases until the voltage reaches such a value that a further increase in applied voltage causes a decrease in the current in the input circuit. Then the voltage in the choke winding 14 suddenly drops, and the voltage across the primary winding 17 increases until it passes through a resonance point, and stabilizes slightly above that point. This occurs at an input voltage less than normal, viz: volts, if the rating of the stabilizer is between 95 and volts input with 118 volts output. The net current flowing through the primary winding 17 is now leading the voltage across the latter so that the primary winding 17 exhibits capacitive reactance. Further increase in input voltage causes a further rapid decrease in current, resulting in a much greater voltage drop across the choke winding 14, with only a small increase in voltage across the primary winding 17, but a substantial change in the phase angle, since it becomes more capacitive. Thus, the stabilizing range is established. Since there is still about a five percent in-.

crease in the output voltage across the operating range, the winding 15 develops a small voltage which is supplied into the output circuit with such polarity that it compensates for this increase, resulting in an output voltage varying less than one percent while the input voltage is varying between 95 and 130 volts. The operation described in the foregoing is conventional.

In the usual stabilizer of this type, 25% third, 9% fifth, 0.7% seventh, and traces of higher odd harmonic voltages are generated. These are undesired, and are greatly reduced by this invention. In this invention, the capacitor 26, the choke winding 16 and the winding 20 form a series circuit across the primary winding 17 which is to be considered not as a part of this circuit but a voltage generator feeding this circuit, which series circuit is resonant at the third harmonic of the line frequency. Odd harmonic voltages are generated in this series circuit, which are out-of-phase with the undesired odd harmonic voltages, thus greatly reducing the latter. While this is also accomplished by the stablizer disclosed in my previously mentioned joint Patent No. 2,505,620, the stabilizer of that patent requires in its simpliest form, two chokes and two capacitors to accomplish what this invention accomplishes with one choke and one capacitor.

The voltage step-up winding 20 provides a higher voltage at the capacitor 26 than would be provided if it were not used, and thereby enables a smaller and less expensive capacitor to be used.

Another feature of this invention resides in using but a single laminated core for all of the windings of its stabilizer and harmonic reducing circuits, instead of the several cores required in prior circuits performing the same functions. Through the choke winding 16 being inductively coupled to the primary winding 17, the odd harmonic current flowing through the choke winding 16 opposes and aids in decreasing the undesired odd harmonic current flowing through the primary winding 17,

The embodiment of this invention shown by FIG. 2 is essentially the same as that shown by FIG. 1, and operates in essentially the same manner. In FIG. 2, the voltage step-up winding 20 instead of being connected to the primary winding 17, is connected to the secondary winding 18, and the choke winding 16 instead of being connected to the primary winding 17, is connected through the winding 15 to the secondary winding 18. The capacitor 26 is, in effect, connected across the secondary winding 18 instead of across the primary winding 17, in a shunt circuit resonant at the line frequency, but, due to the inductive coupling between the primary winding 17 and the secondary winding 18, the capacitor may be considered as connected, in eflfcct, across the primary winding as in FIG. 1. Also, the series circuit of the capacitor 26 and the windings 20 and 16 resonant at the third harmonic frequency, instead of being connected across the winding 17 operating as a generator, is connected across the Winding 18 operating as a generator, but again, due to the inductive coupling between the windings 17 and 18, the series circuit'may be considered as connected across the winding 17.

While the windings could be connected in auto-transformer fashion, it is preferred that they be isolated as shown by FIGS. 1 and 2, thus avoiding the difficulties of common grounds, and dangers of shocks and/or short circuits.

The Patent No. 3,219,916 of H, P. Hart, discloses in FIG. 1, a circuit somewhat similar to that of applicants FIG. 1, but which differs therefrom in that applicants FIG. 1 does not have a winding corresponding to the Winding 8 of FIG. 1 of the Hart patent in a series circuit resonant at the third harmonic frequency; in that FIG. 1 of the Hart patent does not have a winding on his transformer core corresponding to applicants voltage step-up winding 20, and in that the core 9 of the Hart patent is separate from its transformer core 3 (column 2, lines 50-55).

The Patent No. 2,442,214 of T. T. Short discloses in its FIG. 9, a circuit somewhat similar to that of applicants FIG. 1, but which differs therefrom in that it requires an additional winding and an additional capacitor. The Short patent also states in lines 9-11 of column 2 that the cores 3 and 4 may be mechanically joined to form a unitary structure. But while the transformer core 3 shown. by FIG. 3 of the Short patent, taken alone, resembles somewhat applicants single core 9, if the Short core 4 was added to his core 3 to form a unitary structure, such unitary structure would not resemble applicants core 9.

What is claimed, is:

1. A voltage stabilizing and harmonic reducing system, comprising a core having side legs, having a cross portion extending between and connecting said legs, having a first central leg extending from one end of said core between said side legs to said cross portion, said first leg having a relatively wide air gap extending thereacross, said core having a second central leg extending from the opposite end of said core between said side legs to said cross portion, said second leg having a relatively narrow air gap extending thereacross; primary and secondary transformer windings around said second leg; first and second choke windings around said first leg; an input circuit including said first choke winding and said primary winding in series; an output circuit including said secondary Winding; a capacitorrand means connecting said capacitor and said second choke winding in series across one of said transformer windings.

2. A voltage stabilizing and harmonic reducing system as claimed in claim 1 in which there is provided a voltage step-up winding around said second leg, and in which said connecting means includes said step-up windmg.

3. A voltage stabilizing and harmonic reducing system as claimed in claim 2 in which there is provided a voltage compensating winding around said first leg, and in which said output circuit includes said voltage compensating winding in series with said secondary winding.

4. A voltage stabilizing and harmonic reducing system as claimed in claim 1 in which there is provided a voltage compensating winding around said first leg, and in which said output circuit includes said compensating winding in series with said secondary winding.

5. A voltage stabilizing and harmonic reducing system as claimed in claim 4 in which said one transformer winding is said primary winding.

6. A voltage stabilizing and harmonic reducing system as claimed in claim 5 in which there is provided a voltage step-up winding around said second leg, and in which said connecting means includes said step-up winding.

7. A voltage stabilizing and harmonic reducing circuit as claimed in claim 1 in which said one transformer winding is said secondary winding.

8. A voltage stabilizing and harmonic reducing system as claimed in claim 7 in which there is provided a voltage step-up winding around said second leg, and in which said connecting means includes said step-up winding.

9. A voltage stabilizing and harmonic reducing system as claimed in claim 8 in which there is provided a voltage compensating winding around said first leg, and in which said output circuit includes said voltage compensating winding in series with said secondary winding.

10. A voltage stabilizing and harmonic reducing system as claimed in claim 7 in which there is provided a voltage compensating winding around said first leg, and in which said output circuit includes said compensating winding in series with said secondary winding.

References Cited UNITED STATES PATENTS 2,326,465 8/1943 Keeler 323-61 X 2,694,177 11/1954 Sola 323- 2,825,024 2/1958 Berghoff 323---61 2,930,964 3/1960 Goodman 323-48 3,059,172 10/1962 Eissmann et a1 323-61 JOHN F. COUCH, Primary Examiner. W. E. RAY, Examiner. 

1. A VOLTAGE STABILIZING AND HARMONIC REDUCING SYSTEM, COMPRISING A CORE HAVING SIDE LEGS, HAVING A CROSS PORTION EXTENDING BETWEEN AND CONNECTING SAID LEGS, HAVING A FIRST CENTRAL LEG EXTENDING FROM ONE END OF SAID CORE BETWEEN SAID SIDE LEGS TO SAID CROSS PORTION, SAID FIRST LEG HAVING A RELATIVELY WIDE AIR GAP EXTENDING THEREACROSS, SAID CORE HAVING A SECOND CENTRAL LEG EXTENDING FROM THE OPPOSITE END OF SAID CORE BETWEEN SAID SIDE LEGS TO SAID CROSS PORTION, SAID SECOND LEG HAVING A RELATIVELY NARROW AIR GAP EXTENDING THEREACROSS; PRIMARY AND SECONDARY TRANSFORMER WINDINGS AROUND SAID SECOND LEG; FIRST AND 